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1.
A. Ramdani C. Gleitzer G. GavoilleA. K. CheethamJ. B. Goodenough 《Journal of solid state chemistry》1985,60(3)
The distribution of d electrons over the cations in MoFe2O4, which is represented by the formal valence assignment, is shown to be complicated by the equilibrium reactionsFe2+B+Fe3+A+Mo3+Fe3+B+Fe2+A+Mo4+We have used thermal treatment to confirm that the Mo are primarily on octahedral sites; FeA[MoBFeB]O4. K-shell absorption and Mössbauer data at T = 423 K > Tc demonstrate that the iron has an average valence near 2.5+ with fast electron transfer (τh < 10−8 sec) on both octahedral and tetrahedral sites. Paramagnetic susceptibility data give a Curie constant CM = 7.95 ± 0.2 emu/mole and a Weiss constant θp = −445 K; magnetometer measurements confirm a compensation point near 160 K. Transport data give a surprisingly high electronic conductivity, but also give an activated mobility similar to that found in AlFe2O4 and CrFe2O4 where mixed Fe3+/2+ valences on both A and B sites have been demonstrated. However, a positive Seebeck coefficient and a preexponential factor one order of magnitude higher in MoFe2O4 point to involvement of a fraction of the Mo atoms in electronic transport, which would be consistent with the observation of a τh < 10−8 sec on the A sites of a spinel. An energy diagram consistent with these data and other information about the relative redox potentials of these ions in oxides are proposed for this system. 相似文献
2.
Smaail Radi Ahmed Attayibat Abdelkrim Ramdani Maryse Bacquet 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1):232-241
The immobilization of a thiophene-based tripodal ligand, with a donor sulfur, on the surface of an epoxide group containing a silica gel phase for the synthesis of a newly functionalized material based on porous silica-bound bi-thiophene tripodal ligand (SGBT) is described. The modified silica surface was characterized by 13C NMR of a solid sample, elemental analysis, and infrared spectra. This new material was also studied and evaluated by determination of the surface area using the BET equation, the adsorption and desorption capability using the isotherm of nitrogen and BJH pore sizes, respectively. The target material exhibits good thermal stability as determined by thermogravimetry curves. The synthesized material was utilized in column and batch methods for adsorption of Hg2+, Cd2+, Pb2+, Cu2+, Zn2+, K+, Na+, and Li+, and the material exhibits an affinity only towards toxic heavy metals. 相似文献
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K. Ramdani 《Journal of Functional Analysis》2005,226(1):193-229
Let A be a possibly unbounded skew-adjoint operator on the Hilbert space X with compact resolvent. Let C be a bounded operator from D(A) to another Hilbert space Y. We consider the system governed by the state equation with the output y(t)=Cz(t). We characterize the exact observability of this system only in terms of C and of the spectral elements of the operator A. The starting point in the proof of this result is a Hautus-type test, recently obtained in Burq and Zworski (J. Amer. Soc. 17 (2004) 443-471) and Miller (J. Funct. Anal. 218 (2) (2005) 425-444). We then apply this result to various systems governed by partial differential equations with observation on the boundary of the domain. The Schrödinger equation, the Bernoulli-Euler plate equation and the wave equation in a square are considered. For the plate and Schrödinger equations, the main novelty brought in by our results is that we prove the exact boundary observability for an arbitrarily small observed part of the boundary. This is done by combining our spectral observability test to a theorem of Beurling on nonharmonic Fourier series and to a new number theoretic result on shifted squares. 相似文献
5.
Georges Tarrago Abdelkrim Ramdani Jos Elguero Modesta Espada 《Journal of heterocyclic chemistry》1980,17(1):137-142
The n-butylation and N-benzylation of nine pyrazoles bearing different substituents in positions 3 and 5 have been studied in neutral and basic medium (phase transfert catalysis). The orientation of the reaction depends strongly on the method used when the position 3 (or 5) of the starting pyrazole bears a substituent with a lone pair in ortho position (pyrazolyl or pyridyl). The different products have been identified by proton nmr. 相似文献
6.
Smaail Radi Abderrahmane Yahyi Abdelkrim Ramdani Ismail Zidane Brahim Hacht 《Tetrahedron》2006,62(39):9153-9155
The synthesis of a new tetrapyrazolic macrocyclic structure with a functionalised arm is described. The complexing properties of this new compound towards alkali metal ions (K+, Na+, Li+) were studied by liquid-liquid extraction and liquid membrane transport processes. The extracted and the transport cation percentage were determined by atomic absorption measurements and UV spectroscopy. 相似文献
7.
Tabti Hadja Alia Adjdir Mehdi Ammam Abdelkader Mdjahed Baghdad Guezzen Brahim Ramdani Amina Benddedouche Choukry Kamel Bouchikhi Noria Chami Nadir 《Research on Chemical Intermediates》2020,46(12):5377-5390
Research on Chemical Intermediates - A range of Cu-LDHs has been synthesized by co-precipitation using metal nitrate precursors and sodium carbonate under varying molar ratios Cu/Al... 相似文献
8.
We address nonlinear reachability computation for uncertain monotone systems, those for which flows preserve a suitable partial orderings on initial conditions. In a previous work Ramdani (2008) [22], we introduced a nonlinear hybridization approach to nonlinear continuous reachability computation. By analysing the signs of off-diagonal elements of system’s Jacobian matrix, a hybrid automaton can be obtained, which yields component-wise bounds for the reachable sets. One shortcoming of the method is induced by the need to use whole sets for addressing mode switching. In this paper, we improve this method and show that for the broad class of monotone dynamical systems, component-wise bounds can be obtained for the reachable set in a separate manner. As a consequence, mode switching no longer needs to use whole solution sets. We give examples which show the potentials of the new approach. 相似文献
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K. Tebbji H. Oudda B. Hammouti M. Benkaddour S. S. Al-Deyab A. Aouniti S. Radi A. Ramdani 《Research on Chemical Intermediates》2011,37(8):985-1007
The effect of some prepared compounds, namely 3,5-dimethyl-1H-pyrazole (P1), 3(5)-amino-5(3)-methylpyrazole (P2), and 1′,3,5,5′-tetramethyl-1′H-1,3′-bipyrazole (P3), on the corrosion behaviour of steel in 1.0 M hydrochloric acid solution as corrosive medium has been investigated at 308 K using weight-loss measurement, potentiodynamic
polarisation, linear polarisation, and impedance spectroscopy (EIS). Generally, inhibition efficiency of the investigated
compounds was found to depend on the concentration and nature of the inhibitor. P3 was a better inhibitor than P1 and P2,
and its inhibition efficiency increased with increasing concentration of inhibitor, attaining 94% above 10−3
M. Potentiodynamic polarisation studies clearly reveal that P3 acts essentially as a cathodic inhibitor. E (%) values obtained from different methods are in reasonably good agreement. EIS measurements show an increase of transfer
resistance with inhibitor concentration. Partial π-charge on atoms was calculated. Correlation between the highest occupied
molecular orbital energy E
HOMO and inhibition efficiencies was sought. The temperature effect on the corrosion behaviour of steel in 1.0 M HCl without and with different concentrations of inhibitor P3 was studied in the temperature range 308 to 343 K. Thermodynamic
data, for example heat of adsorption (
\Updelta H\textads° \Updelta H_{\text{ads}}^{^\circ } ), entropy of adsorption (
\Updelta S\textads° \Updelta S_{\text{ads}}^{^\circ } ) and free energy of adsorption (
\Updelta G\textads° \Updelta G_{\text{ads}}^{^\circ } ) were calculated by use of thermodynamic equations. Kinetic activation data, for example E
a, ΔH*, ΔS* and pre-exponential factor, were calculated, and are discussed. The inhibiting action of P3 on the corrosion of steel in
1–10 M hydrochloric acid was also studied by weight-loss measurement. The rate constant and reaction constant were calculated for
the corrosion reactions. Adsorption of P3 on the steel surface in 1.0 M HCl follows the Langmuir isotherm model. 相似文献